vibration and shimmying in steering wheel and cab .

[rising sun]

in my case it was the result of mud behind the rotors and discs always give them a wash after driving in the stuff.with a garden hose, since you can flex it to go behind to wash it. i was surprised it could cause such dramatic effects..... although a out of balance wheel could also cause this. in my case the symptoms appeared at a certain speed from 100 to 120 km/hr.